This invention relates to a pattern recognition system for detecting the shape and the position of an object, and more particularly to a pattern recognition system which can recognize an object having a complicated pattern.
Heretofore, a system for recognizing a specific pattern by scanning the pattern to produce a binary signal representative thereof has included means for storing signals representative of a plurality of specific patterns to be used as standard patterns and means for comparing in succession the input binary signal with the standard patterns stored in advance. When they coincide, the input signal at that time is judged to represent the specific pattern.
The prior art system, however, has a number of disadvantages as described hereunder. By way of example, reference is had to a case where a unidimensional input signal pattern, as shown in FIG, 1a, is to be recognized with the prior art system.
In order to recognize a specific pattern in the form of a binary representation a from within a binary signal formed by binary bits "0" and "1", as illustrated in FIG. 1a, a binary representation of a standard pattern b which is shown in FIG. 1b and which corresponds to the specific pattern a to be recognized is employed, and the input signal shown in FIG. 1a and the binary representation of the standard pattern b are compared at every bit position. If, as regards the position at which the standard pattern b exists relative to the input signal, the regions a and b enclosed with broken lines in FIGS. 1a and 1b lie in the illustration relationship, the coincidence between the two can be immediately detected. However, when the standard pattern b shifts rightwards or leftwards relative to the part a of the input signal, the operation of comparing the input signal and the standard pattern must be repeated many times while shifting the standard pattern little by little until the positions of the part a and the standard pattern b come into coincidence. Alternatively, it is necessary to prepare a plurality of standard patterns whose positions are shifted little by little and to perform the process of comparing the plurality of standard patterns and the input signal.
In the above example, the former measure requires a long time for processing. The latter measure makes it necessary to store a plurality of standard patterns beforehand, which leads to the disadvantage of providing a memory of large capacity.
Problems in the prior art will now be described for a case where a two-dimensional specific pattern is recognized. Let's consider a system for recognizing a specific pattern in an object from a signal which is obtained from an image pickup device of, for example, an industrial TV camera. The specific pattern to be recognized is selected, for example, as a rectangular pattern shown as a hatched portion in FIG. 2a. In recognizing such a rectangular pattern with the prior art system, four partial patterns, which are indicated as parts A through D enclosed with broken lines, and which are characteristic shapes of the rectangular pattern, are sampled, and whether or not they are in a proper positional relationship is investigated.
In order to sample the specific pattern in such a system, a standard pattern R.sub.c1 as shown in FIG. 2b (the figure shows only the standard pattern which is employed for recognizing the partial pattern C) is stored beforehand, and the process of finding from within the object a part which coincides most with the stored standard pattern R.sub.c1 is carried out.
In actuality, however, it is sometimes the case that the object to be picked up by the image pickup device is in a rotated and inclined state. In such a case, even when the partial pattern C is included in the object, it cannot be recognized using only the standard pattern R.sub.c1 for the partial pattern C. Therefore, in order to make recognition possible even for such rotation of the object, standard patterns R.sub.c2 shown in FIG. 2c, R.sub.c3 shown in FIG. 2d, etc., with the standard pattern R.sub.c1 rotated by predetermined angles are also prepared and stored beforehand together with the standard pattern R.sub.c1 in the prior art system. Thus, the system can recognize the pattern of a rotated object.
The prior art system which needs to store such standard patterns R.sub.c1 through R.sub.c3 and possibly others in advance requires a memory of large capacity. Therefore, it is high in cost and complicated in processing function.